BOATMAN302

DOES ANYONE HAVE A SETUP SIMILAR TO THIS.1988 311 WITH 502.s, dynoed out at 640 hp. bravo 1,s turning 25 mirage 3 blades at 5000 rpm. naturally aspiated. the owner is seeing 66 mph with the 3 blades and 65 with 24 inch 4 blade bravo1,s. This seems rather wrong.Any imput or opinions.

tony manzella

WHATS THE REV LIMIT SET AT - WHAT GEAR RATIO - STOCK BRVO OR SHORTY - YOUR SPEEDS TAKEN FROM GPS OR SPEEDO- BLADES TURNING IN OR OUT, JUST SOMETHINGS TO START THINKING ABOUT.

got twins ?

That seems way off for the power you have.

I have 330s with bravos, with my 3 blade mirages which are 23s at 4750rpm the best I ever saw on my gps was 63.4 mph but the average was 61.5 mph.
I just bought a new set of props from Brett at BBLADES and they are working awesome.
They are a set of Revolution 4 props. 23 pitch 4 blade ... now that is what is recommended for my horsepower. The props lift the boat better then Hydomotives Quad 4s do and I picked up 6-7 mph in the mid range. THe top end is fairly close if not the same .... but I lost 100-150 rpm on the top end.

I realize I am not a good comparison but .... what i was trying to point out was your numbers aren't that far from mine with alot less horsepower.

A friend of mine repowered his motors last summer he had 420s with TRS drives. He now has 585hp at the prop with the TRS drives and is getting 74mph at wot on gps.

He is using 25 pitch bravo 1 s as props.

I would call Brett at BBLADES and ask him what he thinks ... he has a great program where you can try a set of props for $50.00 without buying them. Great way to get the right prop for your boat and to get what you are looking for.

I decided a long time ago I was done with top end .... there is always going to be someone faster especially with todays technology vs our classic hot rods.
I have been focusing on mid range and cruising speed ... in turn you get the best especially economy and it is better for you motors ( less break down time).

Good Luck !!!!

Jeff

got twins ?

I was reading your post again .....

You don't have enough prop .... those Bravo 1s are actually a 23 pitch in realworld sizing. Mercury calls them a 24 but but in actual reality they are smaller.

That could be a big part of it right there.

This is just a guess from what little experience I have had in testing props and making multiple phone calls to different people in the business.

See if any of your friends have some bigger props to try.

Good luck !!!

Jeff

Ted G

iTrader: (1)

I have stock 502 MPIs running 415 hp, Turn Bravo 1 26 4 blades at 4800 and 71 mph in an 89.

spazboz

iTrader: (2)

That does seem wrong. We JUST finished building 502's for my friends 87' 311. That has 502 MPI motors dyno'ed at 506 hp, 630 lbs of torque. We are looking for mid to upper 70's with the new package. He ran 66 mph with his old stock 420's. Only diff. between your package would be the drives, we are running TRS drives with trannies. I'll let you know our speeds next week with the new power when we sea trial.

RedDog382

My '89 311 had 645 h.p./620 ft lb torque per side and turned a solid 80+ mph with 27p mirage props at 5400 rpm or 28p Bravos at 5250 rpm. Problem with the 27 Mirage was they would blow out when trying to plane off and needed to be feathered quite a bit.

Something in your set-up is wrong or the dyno is lying ...

jaybird

Maybe a few plug wires are off on those motors???

I had supercharged 420's (supposed to have around 550hp) with TRS, Mirage 25's that were cupped and could hit 80 at 5600rpms. Probably could have spun 27's but never got a set to try. Did have to go easy out of the hole to avoid blowout.

Something sounds very wrong with that setup.

BOATMAN302

The numbers are gps numbers,The drives are 1.50.1. im am not sure which direction the props are turning, drives are not shorties, rev limiter is stock. Its not my boat but a friends. I was wondering if the silent thunder box could be hurting him, or maybe the dyno sheets are not correct????? I personally think he should be in the high 70s or early eightys with that kind of power.Mine were dynoed at 595 and 615 and am bouncing off the 90 mark, with surface drives, engines were dynoed at two different places though. I know its frusterating when all that $$$$ is spent and only a few mph,s are gained.

TylerBurich

I get 69 mph at 4850 rpm with stock 25p mirage (non plusses), I also get 69 mph at 5200 rpm with stock mirage (non plusses). My boat is 88 420's trs, only mod is imco exhaust. Numbers are gps